Anomalous clouding behavior of an ethylene oxide-propylene oxide block copolymer in aqueous solution

Partial phase diagram of a polyethylene oxide-polypropylene oxide-polyethylene oxide polymer (EO6-PO30-EO6), pluronic L62, in water, shows two cloud points (CP) in the concentration range (5-25 g dl(-1)). The phase behavior of L62 solutions markedly changes in the presence of neutral salts. While micellization of L62 is not favored by the presence of sodium chloride exerting 'salting out' action, sodium thiocynate which increase CP (salting in) favors micellization of the copolymer. The results of double CP and salt effect are discussed in terms of micellization of the copolymer, The critical micelle concentration (CMC) as determined by surface tension, dye spectral change and hydrodynamic micelle size from dynamic light scattering are reported and compared with similar systems. (C) 2002 Elsevier Science B.V. All rights reserved.